TECHNICAL FIELD
[0001] The present invention relates to a non-woven fabric, and more particularly, to a
non-woven fabric for semipermeable membrane support intended for serving as a support
for membrane production and reinforcing a semipermeable membrane in the production
of a semipermeable membrane having an isolating function, such as an ultrafiltration
membrane, a precision filtration membrane, or a reverse osmosis (RO) membrane.
BACKGROUND ART
[0002] Semipermeable membranes are widely used for the removal of impurities in beverages/industrial
water, desalination of seawater, removal of saprophytic bacteria in foodstuffs, and
a waste water treatment, or in the field of biochemistry and the like.
[0003] For the semipermeable membranes, various polymers such as a cellulose-based resin,
a polyvinyl alcohol-based resin, a polysulfone-based resin, a polyamide-based resin,
a polyimide-based resin, a polyacrylonitrile-based resin, a polyester-based resin,
and a fluororesin are selected in accordance with the use. However, the membrane itself
has weak strength, and cannot endure a high pressure such as 1 MPa to 10 MPa or more
when used alone in ultrafiltration, reverse osmosis or the like. Thus, products in
the form of having a semipermeable membrane formed by applying a resin liquid for
a semipermeable membrane on one surface of a support having high strength and high
liquid permeability, such as a non-woven fabric or a woven fabric, are in use.
[0004] In order to obtain the liquid permeability and filtration performance required for
a semipermeable membrane, it is necessary that a semipermeable membrane be formed
at a uniform thickness on a semipermeable membrane support. Therefore, high smoothness
is required for the surface where a semipermeable membrane will be coated in the semipermeable
membrane support (hereinafter, also referred to as a semipermeable membrane-coated
surface or simply as a coated surface). Furthermore, adhesiveness of the semipermeable
membrane to the support (= anchor effect) is also required. However, if the semipermeable
membrane support is made excessively smooth, when the semipermeable membrane coating
liquid is applied, it becomes difficult for the coating liquid to cling to the support,
adhesiveness of the semipermeable membrane to the support becomes poor, and the semipermeable
membrane becomes easily detachable from the support. To the contrary, when the smoothness
of the support is lowered, it becomes easy for a resin liquid to cling to the support
by the anchor effect, and adhesiveness is improved. However, uniformity of the semipermeable
membrane is deteriorated, and there occurs a problem that the coating liquid to be
applied bleeds into the interior of the support and thereby permeates through to the
non-coated surface. That is, in regard to the smoothness of the semipermeable membrane-coated
surface, uniformity of the thickness of the semipermeable membrane and the adhesiveness
of the semipermeable membrane to the support are in a contradictory relationship.
[0005] It has been suggested to improve the adhesiveness of a semipermeable membrane coating
liquid to a support by roughening the coated surface by adjusting the difference in
the surface roughness between the semipermeable membrane-coated surface of a non-woven
fabric for semipermeable membrane support and a non-coated surface to 15% (see, for
example, Patent Literature 1).
[0006] As a non-woven fabric for semipermeable membrane support, a support based on a bilayer
structure of a front surface layer which uses a fiber having a larger diameter and
has large surface roughness; and a back surface layer which uses a fiber having a
finer diameter and has a dense structure, has been suggested (see, for example, Patent
Literature 2).
[0007] As a non-woven fabric for semipermeable membrane support, there has been suggested
a support characterized by containing two or more kinds of main constituent synthetic
fibers having different fiber diameters and a binder synthetic fiber, and being formed
from a non-woven fabric in which the ratio of smoothness between a semipermeable membrane-coated
surface and a non-coated surface is 5.0:1.0 to 1.1:1.0 (see, for example, Patent Literature
3).
[0008] There has been suggested a support in which the average value of breaking lengths
in the longitudinal direction (MD) and the transverse direction (CD) at the time of
5% elongation is 4.0 km or more, and the degree of air permeability is 0.2 cc/cm
2·sec to 10.0 cc/cm
2·sec (see, for example, Patent Literature 4).
[0009] There has been suggested a support in which adhesiveness to a semipermeable membrane
has been increased by incorporating an atypically shaped cross-section fiber on the
coated surface side layer of the semipermeable membrane (see, for example, Patent
Literature 5).
[0010] There has been suggested a support having a three-layer structure in which an intermediate
layer includes a melt-blown fiber having a fiber diameter of 5 µm or less (see, for
example, Patent Literature 6).
[0011] There has been suggested a support in which prevention of the permeation-through
of a semipermeable membrane coating liquid is attempted by incorporating pulp for
papermaking into a layer on the non-coated surface side of the support having a multilayer
structure (see, for example, Patent Literature 7).
CITATION LIST
PATENT LITERATURE
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0013] The technology of Patent Literature 1 has a problem that since the coated surface
of the support is rough, the thickness uniformity of the semipermeable membrane is
deteriorated.
[0014] The technology of Patent Literature 2 is intended to improve the adhesiveness of
the semipermeable membrane coating liquid to the support by means of the front surface
layer having high surface roughness. However, similarly, this also has a problem that
the thickness uniformity of the semipermeable membrane is deteriorated because the
coated surface of the support is rough.
[0015] In the technology of Patent Literature 3, contrary to Patent Literatures 1 and 2,
the side of the semipermeable membrane-coated surface is smoother than the non-coated
surface. However, since incorporating a fiber having a large diameter generally increases
air permeability of the support and decreases compactness, there is a problem that
even if the smoothness of the coated surface is increased, the thickness uniformity
of the coated semipermeable membrane is not so much improved.
[0016] In the technology of Patent Literature 4, the support has high strength and exhibits
an effect of having small elongation; however, since the semipermeable membrane-coated
surface and the non-coated surface have the same smoothness, the relationship between
the thickness uniformity of the semipermeable membrane and the adhesiveness of the
semipermeable membrane to the support is fundamentally not addressed.
[0017] In the technology of Patent Literature 5, there is a problem that surface unevenness
of the atypically shaped cross-section fiber deteriorates the thickness uniformity
of the semipermeable membrane.
[0018] In the technology of Patent Literature 6, an effect of preventing permeation-through
of the semipermeable coating liquid and an anchor effect can be obtained. However,
since a fiber having a fine diameter is used in the intermediate layer, there is a
problem that air permeability of the support becomes poor.
[0019] In the technology of Patent Literature 7, there is a problem that when the sheet
containing pulp for papermaking is wetted with water upon actual use, the decrement
in the strength of the sheet is increased, and air permeability becomes poor.
[0020] Regarding a non-woven fabric for semipermeable membrane support, there is a demand
for a non-woven fabric in which adhesiveness of a semipermeable membrane to a support
is satisfactory, the thickness uniformity of the semipermeable membrane is satisfactory,
and permeation-through of a coating liquid does not occur. An object of the present
invention is to provide a non-woven fabric for semipermeable membrane support, in
which adhesiveness of a semipermeable membrane to a support is satisfactory, the thickness
uniformity of the semipermeable membrane is satisfactory, and permeation-through of
a coating liquid does not occur.
SOLUTION TO PROBLEM
[0021] A non-woven fabric for semipermeable membrane support according to the present invention
includes a non-woven fabric containing organic synthetic fibers as a primary component,
wherein a semipermeable membrane is to be supported by one surface of the non-woven
fabric, wherein the coated surface to be coated with the semipermeable membrane of
the non-woven fabric and the non-coated surface that is opposite to the coated surface
of the non-woven fabric both have a Bekk smoothness of 5 seconds or more, and the
non-woven fabric has an internal bond strength in the sheet transverse direction in
the range from 0.4 to 0.8 N·m. The sheet transverse direction herein means the width
direction (Cross Direction) of the sheet during the production of the non-woven fabric.
[0022] In regard to the non-woven fabric for semipermeable membrane support according to
the present invention, the non-woven fabric is preferably a wet laid non-woven fabric.
In a wet laid non-woven fabric, since organic synthetic fibers as cut short fibers
constitute a primary constituent element, air permeability of the middle layer is
likely to be increased, and an anchor effect is likely to be exhibited.
[0023] In regard to the non-woven fabric for semipermeable membrane support according to
the present invention, it is preferable that the non-woven fabric before being subjected
to a hot press processing have a single layer structure. When hot press processing
is carried out using a thermal calender, if the non-woven fabric has a single layer
structure, the way of heat propagation is uniform, and accordingly, control of the
pressure drops of the various layer regions based on the processing conditions can
be easily implemented.
[0024] In regard to the non-woven fabric for semipermeable membrane support according to
the present invention, it is preferable that the organic synthetic fibers contain
a main constituent fiber and a binder fiber, and the mixing ratio of the main constituent
fiber to the sum of the main constituent fiber and the binder fiber {main constituent
fiber/(main constituent fiber + binder fiber)} is 50% by mass or more and lower than
100% by mass. It is possible to conduct melt adhesion of the fibers at a lower temperature
than the melting point of the main constituent fiber.
[0025] In regard to the non-woven fabric for semipermeable membrane support according to
the present invention, it is preferable that, when the non-woven fabric to be coated
with a semipermeable membrane is divided, in the thickness direction, into a coated
layer region on the side on which the semipermeable membrane is to be disposed, a
middle layer region, and a non-coated layer region on the side opposite to the surface
on which the semipermeable membrane is to be disposed, the degree of thermal melting
of the organic synthetic fibers in the middle layer region be lower than the degree
of thermal melting of the organic synthetic fibers in the coated layer region and
the non-coated layer region. By bringing the middle layer region of the non-woven
fabric into a semi-molten state, while making the degree of thermal fusion of the
organic synthetic fibers in the coated layer region and the non-coated layer region
higher than that of the middle layer region, compactness of the surface is attained
in any of the semipermeable membrane-coated surface or the non-coated surface.
[0026] In regard to the non-woven fabric for semipermeable membrane support according to
the present invention, any one surface of the non-woven fabric may serve as semipermeable
membrane-coated surface.
[0027] In regard to the non-woven fabric for semipermeable membrane support according to
the present invention, it is preferable that the fibers incorporated into the non-woven
fabric be organic synthetic fibers.
[0028] The non-woven fabric for semipermeable membrane support according to the present
invention includes an embodiment in which the organic synthetic fibers include a main
constituent fiber, and the main constituent fiber is one kind of polyester main constituent
fiber.
EFFECT OF THE INVENTION
[0029] According to the present invention, a non-woven fabric for semipermeable membrane
support, in which adhesiveness of the semipermeable membrane to the support is satisfactory,
the thickness uniformity of the semipermeable membrane is satisfactory, and permeation-through
of a coating liquid does not occur, can be provided. Namely, by relatively decreasing
the thermal fusion bonding properties of the organic synthetic fibers in the middle
layer region of the non-woven fabric with respect to the thickness direction of the
non-woven fabric, the anchor effect of the resin coating liquid is improved, and the
adhesiveness to the support of the semipermeable membrane becomes fine. Since the
thermal fusion bonding properties of the organic synthetic fibers in the coated layer
region of the non-woven fabric are not low as in the middle layer region, the smoothness
of the coated surface is maintained. Since the thermal fusion bonding properties of
the organic synthetic fibers in the non-coated layer region on the opposite side of
the coated layer region are not low as in the middle layer region, the permeation-through
of the semipermeable membrane coating liquid can be prevented. Therefore, it has become
possible to produce a non-woven fabric for semipermeable membrane support that has
never been present before.
DESCRIPTION OF EMBODIMENTS
[0030] Hereinafter, the present invention will be described in detail by way of exemplary
embodiments, but the present invention is not intended to be construed to be limited
by these descriptions. As long as the effect of the present invention is provided,
the exemplary embodiments may include various modifications.
[0031] The non-woven fabric for semipermeable membrane support according to the present
exemplary embodiment is a non-woven fabric containing organic synthetic fibers as
a primary component, wherein, in the non-woven fabric for semipermeable membrane support,
a semipermeable membrane is to be supported by one surface of the non-woven fabric,
wherein the coated surface to be coated with the semipermeable membrane and the non-coated
surface that is opposite to the coated surface of the non-woven fabric both have a
Bekk smoothness of 5 seconds or more, and the non-woven fabric has an internal bond
strength in the sheet transverse direction in the range from 0.4 to 0.8 N·m.
[0032] The organic synthetic fibers, which are primary constituent element of the non-woven
fabric that serves as a semipermeable membrane support, can be divided into a main
constituent fiber and a binder fiber.
[0033] Examples of the main constituent fiber include fibers spun from synthetic resins
such as polyethylene, polypropylene, polyacrylate, polyester, polyurethane, polyvinyl
chloride, polyvinylidene chloride, polyethylene fluoride, polyaramid, polyimide, polyacrylonitrile
and nylon. Furthermore, regenerated celluloses such as rayon; cellulose derivatives
such as cellulose acetate and nitrocellulose; pulp of synthetic resins such as polyethylene,
polypropylene, acrylic and aramid; or fibers produced from natural products as the
raw material sources, such as polylactic acid, polybutyric acid and polysuccinic acid,
which are being actively studied in recent years for biochemical applications, are
also included in the scope of the organic synthetic fibers. Among the synthetic fibers
described above, polyester fibers are suitably used in view of heat resistance, chemical
resistance, fiber diameter, the abundance of the kind of properties, or the like.
Here, in the present invention, among the organic synthetic fibers, an organic synthetic
fiber which is not intended for melt adhesion at a low temperature and has a conventional
melting point, for example, a melting point of 140°C to 300°C, is referred to as "main
constituent fiber." Depending on the shape of the main constituent fiber, when a fiber
having a fine fiber diameter is used, the pore diameter of a completed sheet is further
decreased, and when a fiber having a large fiber diameter is used, the strength of
the sheet is increased. When a short fiber is used, dispersibility in water during
a wet papermaking process is enhanced, and when a long fiber is used, the strength
of the sheet is increased. In the present exemplary embodiment, a synthetic fiber
having a fiber thickness of from 0.05 decitex to 5.0 decitex, and preferably from
0.1 decitex to 3.0 decitex, and having a length of from 1 mm to 8 mm, and preferably
a length in the range from 3 mm to 6 mm, is suitably used. Furthermore, the cross-sectional
shape of the fiber can be appropriately selected as necessary, and is not limited
in the present exemplary embodiment.
[0034] A binder fiber is mixed with the main constituent fiber for the purpose of enhancing
the strength properties of manufactured products, or maintaining a sufficient sheet
strength between a sheet-forming process and a winding process. Here, the "binder
fiber" refers to an organic synthetic fiber in which the melting point of the fiber
as a whole or the fiber surface (sheath portion) is lower by about 20°C, or by 20°C
or more, than the melting point of the main constituent fiber, and has an effect in
which the fiber surface or the fiber as a whole undergoes melt adhesion as a result
of heating by a drying process after papermaking or a thermal pressing process, and
thereby physical strength is imparted to the sheet.
[0035] Regarding the binder fiber, there are available a type in which the entire constituent
resin has a low melting point, and a type having a double structure having an inner
side and an outer side, that is, a so-called core-sheath structure, in which only
the surface is fused, and all of these can be used in the present exemplary embodiment.
Suitably, an unstretched polyester fiber having a melting point of from about 200°C
to 230°C is used. Furthermore, the fiber thickness, length, shape of the cross-section,
and the like can be selected according to the purpose, similarly to the main constituent
fiber. For example, according to the present exemplary embodiment, a binder fiber
having a fiber thickness of from 0.1 decitex to 5.0 decitex, and preferably from 0.5
decitex to 3.0 decitex, and a length of from 1 mm to 8 mm, and preferably a length
in the range from 3 mm to 6 mm, is suitably used. It is preferable that the binder
resin have a resin composition which is the same as or close to the resin composition
of the main constituent fiber; however, different kinds of resin compositions can
also be used in accordance with the required characteristics. Furthermore, a vinylon
binder fiber having a characteristic of melting under humid and hot conditions is
also suitably used.
[0036] Exemplary embodiments of the present invention include a case in which only a main
constituent fiber is incorporated as an organic synthetic fiber, and a case in which
both a main constituent fiber and a binder fiber are incorporated. In the present
exemplary embodiment, the ratio (mass ratio) of the main constituent fiber and the
binder fiber is preferably in the range of from main constituent fiber:binder fiber
= 100:0 to 50:50, more preferably in the range from 80:20 to 55:45. When a sheet containing
only a synthetic fiber that serves as the main constituent fiber, without any binder
fiber mixed therein, is subjected to hot press processing, strands of the main constituent
fiber can be caused to melt-adhere with each other; however, since the main constituent
fiber is not intended for melt adhesion at a low temperature, it is necessary to raise
the heating temperature at the time of hot press processing to a temperature close
to the melting point of the main constituent fiber. When a binder fiber is incorporated
into the main constituent fiber, fiber strands can be caused to melt-adhere with each
other at a temperature lower than the melting point of the main constituent fiber.
However, if the ratio of the binder fiber is more than 50%, since the physical strength
of the binder fiber itself is weaker than the physical strength of the main constituent
fiber, the physical strength of the sheet (hereinafter, may be described simply as
"strength") is decreased.
[0037] Among the fibers to be incorporated, the organic synthetic fibers are employed as
the main constituent fiber of the non-woven fabric by adjusting the mixing ratio of
the organic synthetic fibers to 50% by mass or more, and preferably 70% by mass or
more. At this time, if necessary, pulp-like raw materials, for example, cellulose-based
pulp such as wood pulp for papermaking or cotton linter; inorganic fibers such as
glass fiber, silica fiber and alumina fiber; inorganic filler materials such as calcium
carbonate, talc and kaolin; or the like can also be incorporated in addition to the
organic synthetic fibers.
[0038] Regarding the non-woven fabric for semipermeable membrane support, for example, a
wet laid non-woven fabric that is produced by a wet papermaking method is used. Alternatively,
a dry type non-woven fabric can also be used. Among these, according to the present
invention, a wet laid non-woven fabric provides the effect of the present invention
more effectively than a dry type non-woven fabric does. This is because, as compared
with a dry type non-woven fabric in which organic synthetic fibers as continuous long
fibers constitute a main constituent element, a wet laid non-woven fabric in which
organic synthetic fibers as cut short fibers constitute a main constituent element,
is likely to have high air permeability of the middle layer, and is likely to exhibit
an anchor effect.
[0039] The non-woven fabric before being subjected to hot press processing is such that
the effect of the present invention is exhibited by any of a single layer structure
or a multilayer structure having two or more layers superimposed. A non-woven fabric
having a multilayer structure before being subjected to hot press processing may be
formed of the same raw material in all the layers, or may be formed from different
raw materials, as long as the effect of the present invention is not impaired. Furthermore,
even with the same raw material, the fiber diameter and the fiber length of the organic
synthetic fibers can be changed. When hot press processing is carried out using a
thermal calender, if the non-woven fabric has a single layer structure, the way of
heat propagation is uniform, and accordingly, control of the pressure drops of the
various layer regions based on the processing conditions can be easily implemented.
On the other hand, if the non-woven fabric has a multilayer structure, heat propagation
may be changed at the dislocation parts where layers are brought into contact, and
the control of pressure drop may not be achieved effectively.
[0040] Regarding the method for producing a wet laid non-woven fabric, a so-called wet papermaking
method in which organic synthetic fibers as raw materials are dispersed in water,
subsequently the fibers are laminated on a papermaking wire, dehydrating the fibers
through the lower part of the wire, and thereby forming a sheet, is used. Among others,
a wet laid non-woven fabric according to a wet papermaking method is particularly
preferred because the network of constituent fibers is likely to be formed more uniformly
than a dry type non-woven fabric. The kind of the papermaking machine used in the
wet papermaking method is not limited in the present exemplary embodiment, and for
example, a single-sheet papermaking apparatus, or in the case of a continuous papermaking
machine, a Fourdrinier papermaking machine, a short wire papermaking machine, a cylindrical
wire papermaking machine, an inclined wire papermaking machine, a gap former, and
a delta former can be used.
[0041] Since a sheet obtained after papermaking contains a large amount of water, the sheet
is dried in a drying process. The drying method used at this time is not particularly
limited, but hot air drying, infrared drying, drum drying, drying by a Yankee dryer
and the like are suitably used. The drying temperature is desirably 100°C to 160°C,
and more desirably 105°C to 140°C.
[0042] A wet laid non-woven fabric or a dry type non-woven fabric produced by the methods
described above may be used directly as a semipermeable membrane support, but in many
cases, the strength as a semipermeable membrane support is insufficient. Thus, in
order to obtain a strength sufficient for a semipermeable membrane support, fibers
are thermally welded by subjecting the fibers to hot press processing at a temperature
near the melting point of the main constituent fiber, or a temperature near the melting
point of the binder fiber, and thereby strength is increased. This treatment is carried
out using various hot press processing apparatuses, but generally, a thermal calender
apparatus is effective. For example, a method of using a metal roll nip calender that
is capable of processing at a temperature of 160°C or higher can be used, or if a
resin roll having high heat resistance is available, a metal roll/resin roll soft
nip calender can also be used.
[0043] The temperature conditions for the hot press processing is generally preferably in
the range from 160°C to 260°C, and more preferably in the range from 180°C to 240°C;
however, depending on the kind of the synthetic fibers used, a lower temperature or
a higher temperature may be desirable. For example, when a binder fiber is incorporated
into a main constituent fiber, the fibers are thermally welded by subjecting the fibers
to hot press processing at a temperature near the melting point of the binder fiber,
and thereby strength is increased. The linear pressure is preferably in the range
from 50 kN/m to 250 kN/m, and more preferably in the range from 100 kN/m to 200 kN/m,
but is not particularly limited. Furthermore, in order for the non-woven fabric to
exhibit uniform performance over the entire web, it is desirable to treat the non-woven
fabric with a temperature profile or linear pressure profile that is as uniform as
possible. The roll diameter of the thermal calender apparatus is appropriately selected
depending on parameters such as the base material to be subjected to hot press processing,
the nip pressure, and the speed. When using only a main constituent fiber without
incorporating a binder fiber, the non-woven fabric is subjected to hot press processing
at a temperature near the melting point of the main constituent fiber.
[0044] The method for obtaining the non-woven fabric for semipermeable membrane support
of the present exemplary embodiment is not intended to be limited to the following
method, but one example may be a method of utilizing the relationship between the
fusion temperature and the line speed during the process of thermal fusion of organic
synthetic fibers in the production of a support (non-woven fabric). If the line speed
is relatively slow, heat is conducted to the interior in the thickness direction of
the non-woven fabric, and the coated layer region, the side on which the semipermeable
membrane is to be disposed, the middle layer region and the non-coated layer region,
the side opposite to the surface on which the semipermeable membrane is to be disposed,
are thermally fused uniformly. If the line has a speed exceeding a certain constant
speed, heat cannot be easily conducted to the interior of the non-woven fabric, thermal
fusion in the middle layer region does not proceed, and the middle layer region is
brought to a semi-molten state. However, if the line speed is further increased, thermal
fusion in the middle layer region does not proceed further, and the middle layer region
is almost in an unfused state. As a result, the coating liquid penetrates excessively
into the non-woven fabric and deteriorates the formation of a semipermeable membrane,
and there rises a problem that the non-woven fabric itself is detached in the middle
layer region. In regard to the semi-molten state of the middle layer region, strict
process management should be carried out so that a semi-molten state satisfying the
relationships of the Bekk smoothnesses of the semipermeable membrane-coated surface
and non-coated surface and the internal bond strength in the sheet transverse direction,
which will be described below, would be achieved. Examples of the thermal fusion process
include the drying process of the papermaking process described previously, and hot
press processing, and particularly, the general conditions of the hot press pressing
are important because the conditions are largely affected.
[0045] The present invention makes the thermal fusion bonding state of the fibers in the
middle layer region of the non-woven fabric slack with respect to the coated layer
region and non-coated layer region by utilizing the above-mentioned method and the
like. Specifically, by adjusting the degree of thermal melting of the organic synthetic
fibers in the middle layer region to be lower than the degrees of thermal melting
of the organic synthetic fibers in the coated layer region and non-coated layer region,
the compactness of the middle layer region is lowered, and thus the internal bond
strength in the sheet transverse direction, which acts as an index of the thermal
fusion bonding properties of the organic synthetic fibers that constitute the non-woven
fabric, can be set to be in the range from 0.4 to 0.8 N·m. Furthermore, since it is
necessary to maintain the compactness of the coated layer region and non-coated layer
region, the Bekk smoothness should be at least 5 seconds or more. The Bekk smoothness
can be indices of the thermal fusion bonding properties of the organic synthetic fibers
on the respective surfaces of the coated layer region and the non-coated layer region,
i.e., the semipermeable membrane-coated surface and the non-coated surface.
[0046] The internal bond strength herein is a numerical value measured by an internal bond
tester for evaluating the internal bond strengths of paper and board paper based on
JAPAN TAPPI method for testing paper and pulp No. 18-2: 2000 "Paper and board paper
- Method for testing internal bond strength, Part 2: Internal Bond Tester Method."
The numerical value is obtained by a test method in which a test piece with adhesive
tapes attached to the both surfaces thereon is attached to a sample attaching plate,
and then an impact is provided onto the L-shaped bracket attached to the test piece
by a hammer, and the load at the time when the test piece peels off together with
the L-shaped bracket is measured. The unit is N·m. Since the internal bond strength
is obtained by measuring the strength of peeling from the part where the strength
is weak in the non-woven fabric layer, it can be an index for showing whether the
thermal fusion bonding state of the fibers in the middle layer region of the non-woven
fabric is high or low. The reason why the internal bond strength is in the sheet transverse
direction is that the fiber alignment of a non-woven fabric generally easily becomes
the longitudinal direction, and thus the internal bond strength in the sheet transverse
direction tends to be lower than that in the sheet longitudinal direction, and the
difference in the thermal fusion bonding states of the fibers easily appears.
[0047] In the present invention, the internal bond strength in the sheet transverse direction
is preferably in the range from 0.4 to 0.8 N·m, more preferably in the range from
0.5 to 0.75 N·m. When the internal bond strength is greater than 0.8 N·m, the thermal
melting properties of the fibers in the middle layer region of the non-woven fabric
increase and the middle layer region becomes dense, and thus the semipermeable membrane
coating liquid becomes difficult to permeate into the middle layer region and the
anchor effect of the present invention does not appear. When the internal bond strength
is less than 0.4 N·m, the thermal melting properties of the fibers in the middle layer
region of the non-woven fabric become low and the middle layer region becomes rough,
and thus the semipermeable membrane coating liquid extremely permeates the middle
layer region, and the surface properties (thickness uniformity) of the semipermeable
membrane are deteriorated, and resin permeation-through arises.
[0048] Furthermore, the Bekk smoothness is a test method according to
JIS P 8119: 1998, "Paper and Board Paper - Method for Testing Smoothness by Bekk Smoothness
Tester," and can be measured by using a Bekk smoothness tester. In the present invention,
the Bekk smoothnesses of the semipermeable membrane-coated surface and the non-coated
surface are preferably 5 seconds or more, further preferably 10 seconds or more. When
the Bekk smoothnesses are lower than 5 seconds, the thermal fusion bonding properties
of the organic synthetic fibers in the semipermeable membrane-coated surface and non-coated
surface are deteriorated, and the compactness of the surfaces is lowered. Accordingly,
when the smoothness of the semipermeable membrane-coated surface is lower than 5 seconds,
the fiber melting state of the semipermeable membrane-coated surface is poor, and
the fluff of the fibers penetrates the semipermeable membrane, and thus the surface
properties of the semipermeable membrane are deteriorated. Furthermore, when the smoothness
of the non-coated surface is lower than 5 seconds, the semipermeable membrane coating
liquid that has penetrated into the middle layer region excessively penetrates into
the non-coated layer region, and thus resin permeation-through arises, and the surface
properties (thickness uniformity) of the semipermeable membrane are deteriorated.
Any one of the surfaces of the non-woven fabric may serve as a semipermeable membrane-coated
surface. In the process of coating a semipermeable membrane, management of the front
and the back of the non-woven fabric is made easier. The coated layer region is a
region on the side where a surface that is arbitrary selected from the both surfaces
of the non-woven fabric is coated with the semipermeable membrane, and the non-coated
layer region is a region opposite to the coated layer region. The surface on which
the semipermeable membrane is to be coated is one surface of the non-woven fabric.
[0049] Furthermore, when the Bekk smoothness of the semipermeable membrane-coated surface
is high, the semipermeable membrane coating liquid can be coated more homogeneously,
and the unevenness of the thickness of the semipermeable membrane is decreased and
thus the surface properties of the semipermeable membrane are improved. However, when
the Bekk smoothness is too high, the clinging of the semipermeable membrane to the
surface of the non-woven fabric is deteriorated, and an anchor effect is difficult
to appear, and consequently, the semipermeable membrane easily peels from the non-woven
fabric. At a lower Bekk smoothness, the clinging of the semipermeable membrane to
the surface of the non-woven fabric becomes finer and an anchor effect is exerted
more easily. Namely, the relationship between the Bekk smoothness of the semipermeable
membrane-coated surface and the peeling strength is in a conflicting relationship.
[0050] However, since the middle layer region is in a semi-molten state in the non-woven
fabric of the present invention, even if the Bekk smoothness of the semipermeable
membrane-coated surface becomes relatively high, the coating liquid permeates into
the middle layer region; therefore, an anchor effect is exerted, and thus the semipermeable
membrane and non-woven fabric become difficult to be peeled, and the surface properties
of the semipermeable membrane are also improved at the same time. However, if the
internal bond strength of the non-woven fabric in the sheet transverse direction is
too high, the semipermeable membrane coating liquid is difficult to permeate into
the middle layer region in the case when the Bekk smoothness is high, and thus an
anchor effect is difficult to appear, and the semipermeable membrane easily peels
from the non-woven fabric. Conversely, if the internal bond strength of the non-woven
fabric in the sheet transverse direction is too low, whereas if the Bekk smoothness
is high, the semipermeable membrane coating liquid excessively permeates into the
middle layer region, and thus the surface properties of the semipermeable membrane
are deteriorated. The upper limit of the Bekk smoothness is not limited, but it is
preferably 50 seconds or less, further preferably 40 seconds or less.
[0051] In order to improve the coating adequacy of the semipermeable membrane coating liquid
onto the non-woven fabric, it is also necessary to control the aeration properties
of the non-woven fabric after the hot press processing treatment. In the present invention,
the aeration properties are represented by a pressure drop. The unit is Pa. The pressure
drop is preferably from 50 Pa to 3000 Pa, and more preferably from 80 Pa to 1500 Pa,
as the pressure drop obtainable when the face velocity of the wet laid non-woven fabric
is 5.3 cm/second. If the pressure drop is less than 50 Pa, the semipermeable membrane
coating liquid penetrates excessively to the non-woven fabric, and the surface of
the semipermeable membrane becomes non-uniform, or permeation-through arises. Furthermore,
if the pressure drop is larger than 3000 Pa, to the contrary, since the semipermeable
membrane coating liquid becomes difficult to penetrate into the sheet interior of
the wet laid non-woven fabric, the clinging of the semipermeable membrane to the wet
laid non-woven fabric surface is deteriorated, and the anchor effect of the present
invention is not exhibited.
[0052] In order to make the coating suitability of the semipermeable membrane coating liquid
to the non-woven fabric more satisfactory, it is also necessary to increase the sheet
density of the non-woven fabric that serves as a base material. The sheet density
is preferably 0.5 g/cm
3 or more, more preferably 0.6 g/cm
3 or more, and most preferably 0.7 g/cm
3 or more. If the sheet density is less than 0.5 g/cm
3, the semipermeable membrane coating liquid penetrates excessively to the non-woven
fabric, and the surface of the semipermeable membrane becomes non-uniform, or permeation-through
arises. The upper limit of the sheet density is, for example, 1.0 g/cm
3.
[0053] The grammage of the non-woven fabric is preferably from 30 g/m
2 to 200 g/m
2, and more preferably from 50 g/m
2 to 150 g/m
2. If the grammage of the non-woven fabric is larger than 200 g/m
2, when the semipermeable membrane thus produced is formed into a module, the module
may become excessively thick so that the area per module is decreased, and the filtration
performance may decrease; if the grammage is less than 30 g/m
2, the thickness is excessively small so that there is a risk of the occurrence of
permeation-through of the semipermeable membrane coating liquid in the film-forming
process. Furthermore, the thickness of the non-woven fabric is preferably from 30
µm to 400 µm, and more preferably from 55 µm to 300 µm. If the thickness of the non-woven
fabric is more than 400 µm, when the semipermeable membrane thus produced is formed
into a module, the module may become excessively thick so that the area per module
is decreased, and the filtration performance may decrease; if the thickness is less
than 30 µm, the thickness is excessively small so that there is a risk of the occurrence
of permeation-through of the semipermeable membrane coating liquid in the film-forming
process.
EXAMPLES
[0054] Next, the present invention will be described more specifically by way of Examples,
but the present invention is not intended to be limited to these Examples.
(Example 1)
<Preparation of fiber raw material slurry>
[0055] 22 kg of a commercially available polyester main constituent fiber (trade name: EP133,
manufactured by Kuraray Co., Ltd.) having a fiber thickness of 1.45 decitex and a
cut length of 5 mm, and 8 kg of a commercially available polyester binder fiber (trade
name: TR07N, manufactured by Teijin Fibers, Ltd.) having a fiber thickness of 1.2
decitex and a cut length of 5 mm were introduced into water and were dispersed for
5 minutes using a dispersing machine, to obtain a fiber raw material slurry having
a fiber content concentration of 1% by mass.
<Preparation of fiber slurry>
[0056] Water was added to the fiber raw material slurry 1 to dilute the whole system, and
thus a fiber slurry having a fiber content concentration of 0.03% by mass was obtained.
<Production of sheet>
[0057] This fiber slurry was introduced into a head box of a short wire papermaking machine
to process the fiber slurry for papermaking, and then the fiber slurry was dried with
a cylinder dryer having a surface temperature of 120°C until the sheet completely
dried, to obtain a continuous rolled base paper.
<Hot press processing>
[0058] The rolled base paper was subjected to hot press processing under the conditions
of a roll surface temperature of 185°C, a clearance between rolls of 70 µm, a linear
pressure of 100 kN/m, and a line speed of 20 m/min, using a thermal calender apparatus
with a hard nip of metal roll/metal roll, having a surface length of the metal rolls
of 1170 mm and a roll diameter of 450 mm, and thus a non-woven fabric for semipermeable
membrane support was obtained.
(Example 2)
<Preparation of fiber raw material slurry>
[0059] The process was carried out in the same manner as in Example 1.
<Preparation of fiber slurry>
[0060] The process was carried out in the same manner as in Example 1.
<Production of sheet>
[0061] The process was carried out in the same manner as in Example 1.
<Hot press processing>
[0062] The process was carried out in the same manner as in Example 1, except that the line
speed used in Example 1 was changed to 17 m/min, and thus a non-woven fabric for semipermeable
membrane support was obtained.
(Example 3)
<Preparation of fiber raw material slurry>
[0063] The process was carried out in the same manner as in Example 1.
<Preparation of fiber slurry>
[0064] The process was carried out in the same manner as in Example 1.
<Production of sheet>
[0065] The process was carried out in the same manner as in Example 1.
<Hot press processing>
[0066] The process was carried out in the same manner as in Example 1, except that the roll
surface temperature used in Example 1 was changed to 190°C and the line speed was
changed to 12 m/min, and thus a non-woven fabric for semipermeable membrane support
was obtained.
(Example 4)
<Preparation of fiber raw material slurry>
[0067] The process was carried out in the same manner as in Example 1.
<Preparation of fiber slurry>
[0068] The process was carried out in the same manner as in Example 1.
<Production of sheet>
[0069] The process was carried out in the same manner as in Example 1.
<Hot press processing>
[0070] The process was carried out in the same manner as in Example 1, except that the roll
surface temperature used in Example 1 was changed to 177°C, and the line speed was
changed to 20 m/min, and thus a non-woven fabric for semipermeable membrane support
was obtained.
(Example 5)
<Preparation of fiber raw material slurry>
[0071] The process was carried out in the same manner as in Example 1.
<Preparation of fiber slurry>
[0072] The process was carried out in the same manner as in Example 1.
<Production of sheet>
[0073] The process was carried out in the same manner as in Example 1.
<Hot press processing>
[0074] The process was carried out in the same manner as in Example 1, except that the clearance
between the rolls used in Example 1 was changed to 60 µm, and the line pressure was
changed to 150 kN/m, and thus a non-woven fabric for semipermeable membrane support
was obtained.
(Example 6)
<Preparation of fiber raw material slurry>
[0075] The process was carried out in the same manner as in Example 1.
<Preparation of fiber slurry>
[0076] The process was carried out in the same manner as in Example 1.
<Production of sheet>
[0077] The process was carried out in the same manner as in Example 1.
<Hot press processing>
[0078] The process was carried out in the same manner as in Example 1, except that the clearance
between the rolls used in Example 1 was changed to 60 µm, the line pressure was changed
to 150 kN/m, and the line speed was changed to 17 m/min, and thus a non-woven fabric
for semipermeable membrane support was obtained.
(Example 7)
<Preparation of fiber raw material slurry>
[0079] 15 kg of a commercially available polyester main constituent fiber (trade name: EP133,
manufactured by Kuraray Co., Ltd.) having a fiber thickness of 1.45 decitex and a
cut length of 5 mm, 7 kg of a commercially available polyester main constituent fiber
(trade name: TM04PN, manufactured by TEIJIN LIMITED) having a fiber thickness of 0.1
decitex and a cut length of 5 mm, and 8 kg of a commercially available polyester binder
fiber (trade name: TR07N, manufactured by Teijin Fibers, Ltd.) having a fiber thickness
of 1.2 decitex and a cut length of 5 mm were introduced into water and were dispersed
for 5 minutes using a dispersing machine, to obtain a fiber raw material slurry having
a fiber content concentration of 1% by mass.
<Preparation of fiber slurry>
[0080] The process was carried out in the same manner as in Example 1.
<Production of sheet>
[0081] The process was carried out in the same manner as in Example 1.
<Hot press processing>
[0082] The process was carried out in the same manner as in Example 1, except that the line
speed used in Example 1 was changed to 18 m/min, and thus a non-woven fabric for semipermeable
membrane support was obtained.
(Example 8)
<Preparation of fiber raw material slurry>
[0083] 15 kg of a commercially available polyester main constituent fiber (trade name: EP133,
manufactured by Kuraray Co., Ltd.) having a fiber thickness of 1.45 decitex and a
cut length of 5 mm, 7 kg of a commercially available polyester main constituent fiber
(trade name: EP303, manufactured by Kuraray Co., Ltd.) having a fiber thickness of
3.1 decitex and a cut length of 5 mm, and 8 kg of a commercially available polyester
binder fiber (trade name: TR07N, manufactured by Teijin Fibers, Ltd.) having a fiber
thickness of 1.2 decitex and a cut length of 5 mm were introduced into water and were
dispersed for 5 minutes using a dispersing machine, to obtain a fiber raw material
slurry having a fiber content concentration of 1% by mass.
<Preparation of fiber slurry>
[0084] The process was carried out in the same manner as in Example 1.
<Production of sheet>
[0085] The process was carried out in the same manner as in Example 1.
<Hot press processing>
[0086] The process was carried out in the same manner as in Example 1, except that the line
speed used in Example 1 was changed to 18 m/min, and thus a non-woven fabric for semipermeable
membrane support was obtained.
(Comparative Example 1)
<Preparation of fiber raw material slurry>
[0087] The process was carried out in the same manner as in Example 1.
<Preparation of fiber slurry>
[0088] The process was carried out in the same manner as in Example 1.
<Production of sheet>
[0089] The process was carried out in the same manner as in Example 1.
<Hot press processing>
[0090] The process was carried out in the same manner as in Example 1, except that the roll
surface temperature used in Example 1 was changed to 190°C, and the line speed used
in Example 1 was changed to 5 m/min, and thus a non-woven fabric for semipermeable
membrane support was obtained.
(Comparative Example 2)
<Preparation of fiber raw material slurry>
[0091] The process was carried out in the same manner as in Example 1.
<Preparation of fiber slurry>
[0092] The process was carried out in the same manner as in Example 1.
<Production of sheet>
[0093] The process was carried out in the same manner as in Example 1.
<Hot press processing>
[0094] The process was carried out in the same manner as in Example 1, except that the line
speed used in Example 1 was changed to 30 m/min, and thus a non-woven fabric for semipermeable
membrane support was obtained.
(Comparative Example 3)
<Preparation of fiber raw material slurry>
[0095] The process was carried out in the same manner as in Example 1.
<Preparation of fiber slurry>
[0096] The process was carried out in the same manner as in Example 1.
<Production of sheet>
[0097] The process was carried out in the same manner as in Example 1.
<Hot press processing>
[0098] The process was carried out in the same manner as in Example 1, except that the line
speed used in Example 1 was changed to 10 m/min, and thus a non-woven fabric for semipermeable
membrane support was obtained.
(Comparative Example 4)
<Preparation of fiber raw material slurry>
[0099] The process was carried out in the same manner as in Example 1.
<Preparation of fiber slurry>
[0100] The process was carried out in the same manner as in Example 1.
<Production of sheet>
[0101] The process was carried out in the same manner as in Example 1.
<Hot press processing>
[0102] The process was carried out in the same manner as in Example 1, except that the clearance
between the rolls used in Example 1 was changed to 60 µm, the line pressure was changed
to 150 kN/m, and the line speed was changed to 10 m/min, and thus a non-woven fabric
for semipermeable membrane support was obtained.
(Comparative Example 5)
<Preparation of fiber raw material slurry>
[0103] The process was carried out in the same manner as in Example 1.
<Preparation of fiber slurry>
[0104] The process was carried out in the same manner as in Example 1.
<Production of sheet>
[0105] The process was carried out in the same manner as in Example 1.
<Hot press processing>
[0106] The process was carried out in the same manner as in Example 1, except that the clearance
between the rolls used in Example 1 was changed to 60 µm, the line pressure was changed
to 150 kN/m, and the line speed was changed to 30 m/min, and thus a non-woven fabric
for semipermeable membrane support was obtained.
(Comparative Example 6)
<Preparation of fiber raw material slurry>
[0107] The process was carried out in the same manner as in Example 7.
<Preparation of fiber slurry>
[0108] The process was carried out in the same manner as in Example 1.
<Production of sheet>
[0109] The process was carried out in the same manner as in Example 1.
<Hot press processing>
[0110] The process was carried out in the same manner as in Example 1, except that the line
speed used in Example 1 was changed to 10 m/min, and thus a non-woven fabric for semipermeable
membrane support was obtained.
(Comparative Example 7)
<Preparation of fiber raw material slurry>
[0111] The process was carried out in the same manner as in Example 7.
<Preparation of fiber slurry>
[0112] The process was carried out in the same manner as in Example 1.
<Production of sheet>
[0113] The process was carried out in the same manner as in Example 1.
<Hot press processing>
[0114] The process was carried out in the same manner as in Example 1, except that the line
speed used in Example 1 was changed to 30 m/min, and thus a non-woven fabric for semipermeable
membrane support was obtained.
[0115] The non-woven fabrics for semipermeable membrane support obtained in the Examples
were evaluated by the following methods.
<Measurement of grammage>
<Measurement of thickness and density>
<Measurement of pressure drop>
[0118] The pressure drop obtainable when air was blown to a filtering medium having an effective
area of 100 cm
2 at a face velocity of 5.3 cm/sec by using a self-made apparatus was measured by using
a Manostar Gauge manufactured by Yamamoto Electric Works Co., Ltd. The unit was Pa.
<Measurement of internal bond strength in sheet transverse direction>
<Measurement of Bekk smoothness>
<Formation of semipermeable membrane>
[0121] A sample with an A4 size was cut from each of the non-woven fabrics for semipermeable
membrane support obtained in the Examples, the semipermeable membrane support was
coated with a 20% by mass DMF (dimethylformamide) solution of a polysulfone resin
using a Mayer Bar #12, and the sample was then immersed in water to solidify the coated
membrane, and thus a semipermeable membrane was formed. The film thickness of the
semipermeable membrane was adjusted to 50 µm after drying.
<Peeling strength of semipermeable membrane>
[0122] The above-described samples of the non-woven fabrics for support each having a semipermeable
membrane formed thereon were each passed through the hands 10 times by rubbing with
the hands, and then the peeled state of the semipermeable membrane was evaluated by
visual inspection. A sample in which the semipermeable membrane was completely peeled
from the support was rated as × (having a problem for practical use); a sample in
which signs of peeling of a portion were seen was rated as Δ (level below the lower
limit of practical usability); and a sample in which the semipermeable membrane was
not peeled was rated as ○ (no problem for practical use). Samples rated as ○ and Δ
were regarded as acceptable, and samples rated as × were regarded as unacceptable.
<Surface properties of semipermeable membrane (uniformity of thickness)>
[0123] For each of the above-described samples of the non-woven fabrics for support each
having a semipermeable membrane formed thereon, the surface state of the semipermeable
membrane was evaluated by visual inspection. A sample in which unevenness was observed
on the surface of the semipermeable membrane was rated as × (having a problem for
practical use); a sample in which slight unevenness was observed was rated as Δ (level
below the lower limit of practical usability); and a sample in which no unevenness
was observed was rated as ○ (no problem for practical use). Samples rated as ○ and
Δ were regarded as acceptable, and samples rated as × were regarded as unacceptable.
<Resin permeation-through>
[0124] For each of the above-described samples of the non-woven fabrics for support each
having a semipermeable membrane formed thereon, the state of permeation-through of
the semipermeable membrane coating liquid in the non-coated surface was evaluated
by visual inspection. A sample in which permeation-through was seen at the non-coated
surface was rated as × (having a problem for practical use); a sample in which signs
of permeation-through were seen was rated as Δ (level below the lower limit of practical
usability); and a sample without any permeation-through was rated as ○ (no problem
for practical use). Samples rated as ○ and Δ were regarded as acceptable, and samples
rated as × were regarded as unacceptable.
[Table 1]
|
Example 1 |
Example 2 |
Example 3 |
Example 4 |
Example 5 |
Example 6 |
Example 7 |
Example 8 |
Fiber blend |
PET main constituent 1.45dtex,5mm 22kg/
PET binder 1.2dtex,5mm 8kg |
PET main constituent 1.45dtex,5mm 22kg/
PET binder 1.2dtex,5mm 8kg |
PET main constituent 1.45dtex,5mm 22kg/
PET binder 1.2dtex,5mm 8kg |
PET main constituent 1.45dtex,5mm 22kg/
PET binder 1.2dtex,5mm 8kg |
PET main constituent 1.45dtex,5mm 22kg/
PET binder 1.2dtex,5mm 8kg |
PET main constituent 1.45dtex.5mm 22kg/
PET binder 1.2dtex,5mm 8kg |
PET main constituent 1.45dtex,5mm 15kg/
PET main constituent 0.1dtex,5mm 7kg/
PET binder 1.2dtex,5mm 8kg |
PET main constituent 1.45dtex,5mm 15kg/
PET main constituent 3.1 dtex,5mm 7kg/
PET binder 1.2dtex,5mm 8kg |
Hot press processing |
Roll |
Metal/metal |
Metal/metal |
Metal/metal |
Metal/metal |
Metal/metal |
Metal/metal |
Metal/metal |
Metal/metal |
Temperature ° C |
185 |
185 |
185 |
177 |
185 |
185 |
185 |
185 |
Clearance µm |
70 |
70 |
70 |
70 |
60 |
60 |
70 |
70 |
Linear pressure kN/m |
100 |
100 |
100 |
100 |
150 |
150 |
100 |
100 |
Line speed m/min |
20 |
17 |
12 |
20 |
20 |
17 |
18 |
18 |
Grammage |
g/m2 |
80 |
77 |
78 |
77 |
78 |
78 |
80 |
79 |
Thickness |
µm |
97 |
97 |
99 |
100 |
89 |
90 |
98 |
99 |
Density |
g/cm3 |
0.825 |
0.794 |
0.788 |
0.770 |
0.876 |
0.867 |
0.816 |
0.798 |
Pressure drop |
Pa |
430 |
390 |
450 |
450 |
690 |
740 |
520 |
230 |
Internal bond strength in sheet transverse direction |
N▪m |
0.5 |
0.67 |
0.78 |
0.41 |
0.53 |
0.70 |
0.63 |
0.57 |
Bekk smoothness |
Coated surface |
S |
18.0 |
13.9 |
25.9 |
6.1 |
37.3 |
40.5 |
22.8 |
14.8 |
Same |
Non-coated surface |
S |
19.1 |
13.7 |
23.8 |
6.7 |
38.4 |
40.3 |
21.5 |
15.3 |
Peeling strength of semipermeable membrane |
|
○ |
○ |
○ |
○ |
○ |
○ |
○ |
○ |
Surface properties of semipermeable membrane |
|
○ |
○ |
○ |
Δ |
○ |
○ |
○ |
○ |
Resin permeation-through |
|
○ |
○ |
○ |
○ |
○ |
○ |
○ |
○ |
[Table 2]
|
Comparative Example 1 |
Comparative Example 2 |
Comparative Example 3 |
Comparative Example 4 |
Comparative Example 5 |
Comparative Example 6 |
Comparative Example 7 |
Fiber blend |
PET main constituent 1.45dtex,5mm 22kg/
PET binder 1.2dtex,5mm 8kg |
PET main constituent 1.45dtex,5mm 22kg/
PET binder 1.2dtex,5mm 8kg |
PET main constituent 1.45dtex,5mm 22kg/
PET binder 1.2dtex,5mm |
PET main constituent 1.45dtex,5mm 22kg/
PET binder 1.2dtex,5mm 8kg |
PET main constituent 1.45dtex,5mm 22kg/
PET binder 1.2dtex,5mm 8kg |
PET main constituent 1.45dtex,5mm 15kg/
PET main constituent 0.1dtex,5mm 7kg/
PET bi.d., 1.2dtex,5mm 8kg |
PET main constituent 1.45dtex,5mm 15kg/
PET main constituent 0.1dtex,5mm 7kg/
PET binder 1.2dtex,5mm 8kg |
Hot press processing |
Roll |
Metal/metal |
Metal/metal |
Metal/metal |
Metal/metal |
Metal/metal |
Metal/metal |
Metal/metal |
Temperature° C |
190 |
185 |
185 |
185 |
185 |
185 |
185 |
Clearance µm |
70 |
70 |
70 |
60 |
60 |
70 |
70 |
Linear pressure kN/m |
100 |
100 |
100 |
150 |
150 |
100 |
100 |
Line speed m/min |
5 |
30 |
10 |
10 |
30 |
10 |
30 |
Grammage |
g/m2 |
77 |
76 |
78 |
80 |
78 |
79 |
78 |
Thickness |
µm |
99 |
98 |
100 |
90 |
89 |
98 |
98 |
Density |
g/cm3 |
0.778 |
0.776 |
0.780 |
0.889 |
0.876 |
0.806 |
0.796 |
Pressure drop |
Pa |
420 |
370 |
460 |
830 |
410 |
690 |
370 |
Internal bond strength in sheet transverse direction |
N▪m |
0.94 |
0.32 |
0.83 |
0.82 |
0.33 |
0.89 |
0.35 |
Bekk smoothness |
Coated surface |
S |
41.6 |
3.5 |
33.7 |
51.9 |
16.7 |
38.4 |
17.5 |
Same |
Non-coated surface |
S |
39.7 |
3.7 |
34.1 |
52.6 |
16.5 |
38.1 |
16.6 |
Peeling strength of semipermeable membrane |
|
× |
○ |
× |
× |
○ |
× |
○ |
Surface properties of semipermeable membrane |
|
○ |
× |
○ |
○ |
○ |
○ |
× |
Resin permeation-through |
|
○ |
× |
○ |
○ |
× |
○ |
× |
[0125] The results are summarized in Table 1 and Table 2. From the results of Table 1 and
Table 2, it can be seen that in Example 1 and Example 2 in which the internal bond
strength in the sheet transverse direction was within the defined range, the peeling
strength of the semipermeable membrane, the surface properties of the semipermeable
membrane and the resin permeation-through were at acceptable levels, and an appropriate
degree of the semi-molten state of the middle layer region was obtained. Furthermore,
Example 3 exhibited a difference in the roll surface temperature of the thermal calender,
from Examples 1 and 2; however, it can be seen that when the line speed is appropriately
selected, an appropriate degree of the semi-molten state of the middle layer region
is obtained, and the sample was at an acceptable level. In Example 4, the internal
bond strength in the sheet transverse direction was close to the lower limit of the
defined range, and the melting properties of the middle layer were low and at an acceptable
level, whereas the surface properties of the semipermeable membrane were at a level
below the lower limit of practical usability.
[0126] On the other hand, Comparative Example 1 and Comparative Example 3 are examples in
which the internal bond strength in the sheet transverse direction was higher than
the upper limit, and the peeling strength of the semipermeable membrane was deteriorated.
It is understood that the anchor effect of the semipermeable membrane to the support
was weakened. Comparative Example 2 is an example in which the internal bond strength
in the sheet transverse direction and the Bekk smoothness were lower than the lower
limit, and the surface properties of the coated layer and the resin permeation-through
were deteriorated. It is understood that the semipermeable membrane coating liquid
had penetrated excessively.
[0127] Examples 5 and 6 are examples in which the linear pressure was increased by narrowing
the clearance between hot rolls. As the sheet density increased, the coated surface
and the non-coated surface both had increased smoothness, and there was a concern
about the anchor effect of the semipermeable membrane to the support being weakened;
however, since the internal bond strength in the sheet transverse direction was in
the defined range, the peeling strength of the semipermeable membrane was fine. In
contrast, in Comparative Example 4, the internal bond strength in the sheet transverse
direction was higher than the upper limit, and the peeling strength of the semipermeable
membrane was deteriorated. In Comparative Example 5, the internal bond strength in
the sheet transverse direction was lower than the lower limit, and the resin permeation-through
was deteriorated.
[0128] Example 7 is an example in which the pressure drop was controlled by incorporating
a PET main constituent fiber having a fine diameter to the fiber blend, and Example
8 is an example in which the pressure drop was controlled by mixing and incorporating
a PET main constituent fiber having a large diameter. In both examples, the internal
bond strength in the sheet transverse direction was within the defined range, and
thus the peeling strength of the semipermeable membrane, the surface properties of
the semipermeable membrane, and the resin permeation-through were at acceptable levels.
In contrast, in Comparative Example 6, the internal bond strength in the sheet transverse
direction was higher than the upper limit, and the peeling strength of the semipermeable
membrane was deteriorated. In Comparative Example 7, the internal bond strength in
the sheet transverse direction was lower than the lower limit, and the resin permeation-through
and the surface properties of the semipermeable membrane were deteriorated.